The present invention relates generally to speakerphones, and more particularly to an improved speakerphone that can advantageously be utilized in both radio and landline telephone systems.
In both radio and landline telephone systems, a user communicates by means of a handset that includes a speaker at one end which is placed close to the user's ear and a microphone at the other end which is held close to the user's mouth. Thus, the user has only one free hand since the other must be used to hold the telephone handset. In order to provide a greater degree of freedom to the user, speakerphones have been developed for use in landline telephone systems. A conventional speakerphone is typically coupled to the telephone line and when enabled allows the hands-free party user to freely move about while still communicating with another party. Such speakerphones typically compare the volume of the hands-free party and the other party and select the party speaking the loudest. Furthermore, conventional speakerphones, such as that described in U.S. Pat. No. 3,751,602, always revert to the listen mode a short time interval after the hands-free party stops talking. However, conventional speakerphones suffer from a number of problems including inability to accommodate high ambient noise environments and breakup due to feedback from the speaker to the microphone when the speaker amplification has been turned up. These conventional speakerphones work reasonably well when utilized with landline telephones in relatively quiet surroundings, but may not operate correctly when used in noisy environments and especially when used with a radio due to the high degree of ambient noise encountered in vehicles. For example, a high level of ambient noise may cause such speakerphones to always select the hands-free party.
The problem of accomodating a high degree of ambient noise has been addressed in the speakerphones described in U.S. Pat. Nos. 4,378,603 and 4,400,584 by selecting only one of the parties while totally muting the other party, and switching between parties using the output of audio signal detectors that detect the presence of audio signals only when the audio signals exceed the background noise by a predetermined amount. Another prior art speakerphone totally ignores the hands-free party and always selects the other party whenever audio signals from the other party are detected.
However, none of these prior art speakerphones accomodates both a noisy environment and allows the hands-free party to break in relatively easily on the other party. Accordingly, there is a need for an improved speakerphone that can accomodate noisy environments and allow the hands-free party to break in relatively easily on the other party.